1. Field of the Invention
The invention relates to a laboratory centrifuge and, more specifically, a laboratory centrifuge having a noise abatement system.
2. Description of Related Art
U.S. Pat. No. 3,804,324 is representative of known laboratory centrifuges. In centrifuges of this kind, several buckets are supported radially so they may pivot about tangentially mounted shafts with their centers of gravity outside the shafts.
When the rotor is standing still, the buckets hang down and typically may be loaded with sample liquids, usually in centrifuging vials, for instance at the rate of several vials per bucket, in seats provided for that purpose. As the angular speed rises, the buckets swing outward. The advantage of this design is that the liquid level of the vessels as seen within them remains constant.
The design of this species incurs the drawback of the separate, individual configuration of the buckets, which at higher angular speeds entails strong air turbulence and, hence, strong, interfering noises.
Therefore, the cited known design is fitted with a device, in the form of a closed, sound-absorbing housing, to reduce the bucket-generated noises. This device, however, entails the drawback that the heat generated by the buckets"" air turbulence remains trapped in the housing and leads to undesired heating of the sample liquid. The conventional remedy is refrigeration, whereby, however, costs are substantially increased.
An objective of the present invention is to create a laboratory centrifuge offering a simpler design and lower noise levels.
In the design of the invention, turbulence generators are mounted on the surface of each bucket to interfere with the air flowing by, which heretofore rested in laminar manner against the buckets. Accordingly, as seen in the direction of flow, there is turbulence behind the turbulence generators. As a result there is a significant reduction of the cross-section of the wake behind the buckets. Because of this feature and on account of less interference by the next rotor, there results a significantly reduced noise level.
The invention is based on the assumption to not dampen the noises generated in laboratory centrifuges after they have been generated, but rather to reduce them already as they are being generated, and therefore it exploits the previously overlooked, very old aerodynamic insights that are described in GRENZSCHICHT-THEORIE (Boundary Layer Theory) by Dr. Hermann Schlichting, G Braun publishers, Karlsruhe, Germany, 5th edition, on page 39.
Empirical noise reductions up to 6 dB have been attained by use of the present invention
Turbulence generators may be mounted on the bucket, as seen in the direction of air flow, relatively far ahead and also relatively far to the rear. However, the turbulence generators must be large in order to act in a sufficiently spoiling manner. In accordance with the present invention, high laminar flow is present at the site of maximum bucket diameter. Even very small turbulence generators may be adequately effective in that zone.
Single compact turbulence generators already may abate noise significantly. Advantageously, however, the turbulence generators are elongated or more than one may be used. In accordance with the present invention, the linearly extending turbulence generator system is situated in zones of approximately equal flows and thereby offers an effect that is constant in length.
Turbulence generators may assume the form of recesses in the bucket surface, for instance, holes or an elongated groove. Advantageously, however, because offering substantially larger effects, the turbulence generator shall be in the form of a salient.
A turbulence generator rising above the surface illustratively may be a protruding pin or a collection of protruding pins or also assume the form of a bonded strip of rough sandpaper. Illustratively, a wire soldered to a substrate or a rising bead or the like may offer outstanding effectiveness. In accordance with another feature of the invention, a simple manufacturing technique accordingly is a cylindrical blank milled-out to attain the desired shape.